Technical Abstract:
Ovine herpesvirus-2 (OvHV-2) is a member of the subfamily Gammaherpesvirinae, genus Rhadinovirus. OvHV-2 is the causative agent for sheep-associated malignant catarrhal fever (SA-MCF) in many clinically susceptible ruminant species worldwide. Sheep are the natural carriers of OvHV-2. The inability to propagate OvHV-2 in vitro has severely limited research progress in understanding disease transmission and pathogenesis, and in developing effective programs for control of the disease. A recent study showed that nasal shedding is the predominant mode of OvHV-2 transmission among sheep, which suggests that active viral replication occurs in cells within or associated with the respiratory tract. To determine which tissues contain permissive cells supporting OvHV-2 replication in vivo, samples from infected sheep were collected and analyzed for an RNA transcript (ORF 25, encoding the major capsid protein) expressed during productive viral replication. DNA and total RNA were isolated from nasal swab samples, peripheral blood leukocytes and representative tissues collected from five sheep experiencing a shedding episode, two non-shedding and one uninfected sheep. ORF 25 RNA transcripts were detected in nasal secretions of all OvHV-2 infected sheep experiencing a shedding episode. Although there was no specific pattern of ORF 25 expression in peripheral blood leukocytes or tissue samples, signals were most often detected in the turbinate of animals experiencing a shedding episode. The data support that tissues of the upper respiratory tract of sheep, especially the turbinate, are sites for OvHV-2 replication and that replication is localized within tissues.